Magnetically operated print hammers in high speed printers



NOV- 1, 1966 J. F. KALBACH ETAL 3,282,203

MAGNETICALLY OPERATED PRINT HAMMEHS IN HIGH SPEED PRINTERS Nov. l, 1966KALBACH ETAL 3,282,203

MAGNETICALLY OPERATED PRINT HAMMERS IN HIGH SPEED PRINTERS Filed April16, 1964 5 Sheets-Sheet 2 Nov. 1, 1966 F. KALBACH ETAL 3,282,203MAGNETIGALLY OPERATED PRINT HAMMERS IN HIGH SPEED PRINTERS Filed April16, 1964 3 Sheets-Sheet 5 f/ 505505 "il 1 L asas; his i 7 r k;)

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United States Patent @ffice 3,282,203 Patented Nov. 1, 1966 3,232,203MAGNETICALLY OPERATED PRINT HAMMERS IN HGH SPEED PRHNTERS John FrederickKalhach, Altadena, and Walter Griffin Paige, Pasadena, Calif., assignorsto Burroughs Corporation, Detroit, Mich., a corporaticn of DelawareFiled Apr. 16, 1964, Ser. No. 360,194 15 Claims. (Cl. 10i-93) Thisinvention relates to printing machines and more particularly to animprovement in magnetically operated printing devices for use in highspeed printing machines.

High speed printers are well known which use black printing to impart atype character or mark on paper. A printer which back prints is onewherein a moving hammer strikes the paper being printed and forces itagainst a type character carried on a revolving dnum or the like. Thetype character may have ink thereon or carbon paper may be placed, forexample, between the paper and the drum for making the actual mark onpaper.

There are a number of different devices for actually forcing the hammeragainst the type character. For example, in a first prior art printer, asolenoid is used to actuate print hammers, through a series ofmechanical linkages, against a rotating drum. Such an arrangementsuffers from the serious disadvantage that it is slow due to the mass oflinkages which must be moved and due to the inherent play in connectionsbetween linkages. Additionally, this first prior art printer is quitelarge due to the fact that the solenoids must be staggered in a planenormal to the line of print at different positions in the machine inorder to allow enough clearance to mount the solenoids and to allowclearance for operation of the solenoids and the connected linkages.Further, the printer is quite heavy due to the fact that relativelylarge and heavy solenoids are required to move the linkages and thehammers and due to the weight of the many linkages required.

Other staggering arrangements of the solenoids have been devised. Forexample, solenoids have also been lstaggered above, below and radiallyfrom the line of print.

An improved prior art printer over the first prior art printer is onewherein a plurality of printing hammers are positioned adjacent arotating drum, each of the printing hammers comprising an elongatedshank having an electrically energizable current carrying coil connectedintermediate the ends of the shank. An array of U shaped magnets areprovided to cause printing hammers, having excited coils, to be movedtowards the type drum for printing. The magnets are made of a magneticmaterial commonly referred to as ALNICO V. A separate pair Iof U Ishapedmagnets is required for each current carrying coil and the array ofmagnets are staggered in depth, normal to the surface of the drum. Forexample, there may be as many ias six rows of staggered magnets.

The improved prior art printer has many desirable features over thefirst prior art printer. For example, the weight and size of theprinting machine is reduced due to the elimination of the heavysolenoids and linkages. However, the improved prior art printers suffersfrom the disadvantage that the magnets must be staggered in depth inorder to allow the printing hammers to be poistioned close enoughtogether for printing a complete line of print. The reason thatstaggering is required is that normally it is desired to print tencharacters per inch in a line of print. Thus, a printing hammer spacingof .l inch spacing on center is required. A printing hammer spacing of.1 inch on center cannot be achieved with U shaped magnets withoutstaggering the magnetic elements. One disadvantage of having a staggeredarray is that the printing 'hammers must be long enough to acdwell timeincreases.

commodate a coil for each row of magnets in the staggered array, therebygreatly increasing the lengths of the hammers and thereby increasing thedwell time of the hammer during an impact with the drum. The speed ofoperation of the printer is dependent in large upon the dwell time ofthe hammers, and the speed decreases as The present invention greatlyimproves the operation of the improved prior art high speed printingapparatus. For example, one embodiment of the present invention iscapable of operating at a speed of 3000 lines per minute, whereas theimproved prior art printer is only capable of printing at a speed of 300lines per minute. Accordingly, this embodiment of the present inventionaffords Ian increase in speed by a factor of approximately 10. Inaddition, the weight and overall size of the aforementioned embodimentof the present invention is markedly reduced as compared with theimproved prior art printer. Further, both the cost and complexity of theaforementioned embodiment of the present invention are reduced incomparison with the improved prior art printer. Also, the presentinvention eliminates the need for a separate pair of magnets per coil.

A very significant improvement in an embodiment of the present inventionis that the need for staggering of the solenoids or actuating devices iseliminated. The actuating devices or means are arranged in a straightline parallel with the axis of the print drum.

Briefiy, a specific embodiment of the present invention comprises, arotatable type drum and a plurality of hammer assemblies. Each hammerassembly comprises an elongated member having a hammer tip at one endthereof and a substantially flat coil mechanically connectedintermediate the ends of the elongated member with the axis of the coilperpendicular to the member, also provided are means for supporting theelongated members and the vconnected coils with the coils spaced a shortprefixed distance apart and in a substantially straight row parallelwith the axis of the drum, the mounting means is adapted to allow thehammer assemblies to move t-he hammers thereof into a printing positionwith respect to the drum. A pfarallelepiped shaped ceramic magnet havinga thin dimension positioned in between each adjacent pair of coils isalso provided. The magnets are magnetized through the t-hin dimension ina direction parallel with the axes of said coils suc-h that a magneticinteraction is caused which forces a coil to move, in the correspondinggap, so that the connected hammer tip is forced into a printing positionwith respect to the drum, in response to current applied in theparticular coil.

Stated another way, an embodiment of the present invention comprises, aplurality of permanent magnets positioned in a substantially straightrow. Each of the magnets has a pair of parallel surfaces separated by athin dimension which face the adjacent magnet, at both sides, to defineslot-shaped gaps therebetween. A hammer assembly is provided for eachgap comprising a hammer tool and a substantially fiat coil mechanicallyconnected to the hammer tool. Means is provided which is adapted forsupporting the hammer assemblies with the laxes of the coils thereof ina substantially straight line perpendicular to the surfaces of themagnets such that the coils are free to move in the corresponding gapstoward and away from a predetermined point of impact. The magnets aremagnetized through the thin dimension thereof parallel with the axes ofthe coils such that a north pole magnetic field is formed in one gap anda south pole magnetic field is formed in the adjacent gap. All of themagnets are magnetically poled in one direction along one side of therow of magnets and in the opposite direction along the opposite side ofthe row of magnets. The coils are positioned in relation to `the polesof the magnets such that a force is caused between a coil and thecorresponding magnets, responsive to current applied in the coil, forforcing the connected hammer tool into such point of impact.

These and other aspects of the present invention may be morefullyunderstood with reference to the following description of the figures ofwhich:

FIG. 1 is an enlarged side elevation view of a printer, with a portionof the housing `and drum broken away, and embodying the presentinvention;

FIG. 2 is an enlarged cross-sectional -view of the printer shown in FIG.l and is taken along the lines 2-2 of FIG. 1;

FIG. 3 is a side elevation view of the printing hammer assembly shown inthe printer of FIGS. 1 and 2;

FIG. 4 is a cross-sectional view of the coil of the-hammer assemblyshown in FIG. 3 and taken along the lines 4-4 of FIG. 3;

FIG. 5 is a side elevation view of the lower row of coils and lower rowof magnets in FIG. 1, with the rest of the printer broken away inorderto illustrate the relationship between the coils of the hammerassemblies and the magnets which are used in printer of FIGS. 1 and 2'.FIG. 5 also illustrates the active magnetic area of the magnets by dots;

FIG. 6 is a cross-sectional view of the rst four magnets in the lowerrow and the corresponding three coils taken along the lines 6-6 of FIGS.5. FIG. 6 also illustrates the active magnetic area of the magnets, bydashed lines,

-and shows the north and south poles of the magnets using theabbreviations N and S;

. 4 between hammer tips of the rows of hammer assemblies 100 and 300 andthe type drum 10. A web of carbon paper 12a is placed next to the paper12b so that when a Vhammer strikes the paper 12b a type character, onthe mer assemblies 100 and 300 and the type drum 10. Ribbon shields 16,18, and 22 are connected by means (not shown) to the printer frame andare used in a conventional manner well known in the printer art forguiding the paper and carbon paper.

The paper 12b and carbon paper 12a may be moved continuously orintermittently, by means (not shown) which is well known in the printerart.

FIG. 7 is a side view of one of the magnets shown in FIG. 5;

FIG. 8 is a sketch of a portion of the improved prior are printingdevice showing a top elevational view of three coils positioned inbetween the poles of three pairs of U shaped magnets, and shown with theelongated hammer shank removed. FIG. 8 is a cross sectional view of thecoils and magnets of the improved prior art printing device vtakensimilar to the view of the present invention in FIG. 6; and

FIG. 9 is a side elevational view showing the edge of a portion of oneof the at spring supports for the hammer assemblies, shown in FIG. l.

FIG. 10 is a pictorial view of five of the magnets shown in FIG. 1 alongwith a portion of the module base 24 illustrating the manner in whicheach is securely fastened in between a pair of rigid and parallelmembers and thereby held parallel to ea-ch other.

Refer now to the enlarged view of the printer shown in FIGS. l and 2 andembodying the present invention. FIG. 1 shows a rotatable type drum 10having a plurality of rings of type (not shown) around the peripherythereof. The type in the rings are aligned in rows so that likecharacters (i.e. all As), for a single line of print, may be typed outat the same time in parallel. The drum has an axis, illustrated by a dot10a in FIG. 1, extending perpendicular to the surface of the paper inFIG. 1. The dot 10a is not shown at the true center of the drum 10 butis shown as positioned in FIG. 1 for illustration purposes. The typedrum 10 is rotated by a suitable driving motor (not shown) in a mannerwell known in the printer art. The drum 10 is typically rotated at aspeed of from 300 to 1500 r.p.m.

Although a type drum is shown as the type bearing means, by way ofexample, it should be understood thatl the present invention is equallyapplicable to other type bearing means, such as a type bearing chain, amoving type box, or other devices having type thereon. It should also beunderstood that the type bearing means could be moved on demand, ratherthan continuously.

A lower row of print hammer assemblies 100 and an upper row of printhammer assemblies 300 are shown for striking a-sheet of paper 12bwhich'is positioned in Magnetic means is providedfor cooperating withthe hammer assemblies in rows and 300 for causing printting operationsto take place. The magnetic means for row 100 include a plurality ofsolid parallelepiped shaped magnets positioned in a substantiallystraight row 200 parallel with the axis 10a of the type drum 10. Anupper row of solid parallelepiped shaped magnets are similarlypositioned in a straight row 400 parallel with the axis of the drum 10for actuating the row of hammers 300.

Eleven magnets are shown in the lower row 200. Moving from right to leftin FIG. 2 the magnets are referenced by the symbols 201 through 211(only the first two magnets 201 and 202 and the last magnet 211 in therow are shown with reference numbers in FIG. 2). Each of the magnets hasa pair of parallel and substantially at surfaces arranged with respectto the adjacent magnet, yat both sides, to define slot-shaped gapstherebetween. Moving from right to left in FIG. 2, the slot-shaped gapsare referenced by the symbols 101a through l10n, which bear numberscorresponding to numbers of corresponding hammer assemblies positionedthereat with the letter a followingthe numbers to designate thereference to the gap as opposed to the hammer assembly (only the firsttwo and the last magnet in the row are shown with reference numbers inFIG. 2).

The row of magnets 200 is anchored in the printer by means of a modulebase 24 and the frame 25. The modrule base 24 is attached to the frame25 by means of a bolt 24b which is threaded into a riser member 24C, apart of the module base 24. The riser 24e fits into a recess formed inthe frame 25.

With reference to FIG. 10, which shows a pictorial view of the magnetsfastened into the module base 24, it will be seen that there is a pairof parallel support arms 205a upstanding at eitherl side of the magnet205. The parallel support arms 205a are dimensioned and positioned solthat the gaps at either side remain unobstructed. There is an Identicalpair of rigid and parallel support arms 201:1 through 204g and 20601through 211a for each of the magnets 201 through 204 and 206 through211. Only one arm of the pair of arms 201a through 204a is shown 1n FIG.10. Also, only magnets 201 through 205 are shown in FIG. 10. Each of themagnets 201 through 211 1s securely cemented by means of an epoxy cement(not shown) in between the corresponding pair of support arms.

y It is well known that magnets exert forces when positroned in closeproximity to each other. A feature of the present invention is that theforces on each of the magnets 1n each row starting with the secondmagnet from each end and moving towards the center have equal andopposrte forces acting thereon, due to the polarity of the adjacentmagnets. However, the magnets at the ends of the rows have unequalmagnetic forces acting thereon and the forces are quite significant. Themagnetic forces pull and tend to move the end magnets toward theadjacent magnet. Therefore, it is necessary to provide a structure whichrigidly holds the end magnets in position. To this end the support armsare rigidly formed as a part of the base structure 24 so as to holdthemagnets in place parallel to each other.

The row of hammer assemblies 100 include ten hammer asemblies which,moving from left to right in FIG. 2, are referenced by symbols 101through 110 (only the rst two hammer assemblies 101 and 102 and the lasthammer assembly 110 bear reference symbols. in FIG. 2). Thus, one hammerassembly is provided for each of the gaps 1010 through ln. Each hammerassembly comprises an elongated member having a hammer tip at one end, asubstantially flat coil mechanically connected intermediate the ends ofthe member with the axis of the coil perpendicular to the elongation ofthe member and means for supporting each hammer assembly such that thecoil is free to move in the corresponding gap toward and away from thesurface of the drum.

Refer now to FIGS. 3 and 4 which show a side elevation view of thehammer assembly 101 and a cross-sectional view of the coil. Theelongated member is shown generally at 120 with a hammer tip at the end121. A coil 124 and protective shields 125 and 126 are shown generallyat 122 and are mechanically connected intermediate the ends 121 and 123of the elongated member 120.

The coil 124 is generally rectangular shaped, and is made out of aflattened ribbon-like wire which is coated with a nonconductive coatingto prevent shorting between turns. All the windings lie in a singleplane parallel with the elongation of the elongated member 120. Thus,the coil is flat and its axis is perpendicular to the elongation of theelongated member 120. The protective shields 126 and 125 surround thecoil 124 and provide a rigid support for the coil 124 for the purposedescribed.

The elongated member 120 has a slit running down the length thereof intowhich the assembly 122 is inserted. The assembly 122 is secured in theslit of the elongated member 120 by means of an epoxy cement (notshown).

The supporting means for the hammer assembly 101 includes a pair of flatsprings 127 and 128. The springs 127 and 128 are mechanically connected,parallel to each other, between a point adjacent to the ends 121 and 123of the elongated member 120 and a hammer assembly base structure 129.The springs 127 and 128 extend into circular perforations 130 and 131which are formed in the elongated member 120. Epoxy lis molded into thecircular perforations 130 and 131 so asto securely attach the springs tothe elongated member 120. The opposite ends of the springs 127 and 128are embedded in the base structure 129 which is molded out of a suitablerigid plastic or other nonconductive material.

The springs 127 and 128 not only support the elongated member 120 but inaddition provide an electrical current path to and away from the coil124. To this end, the springs are preferably made out of at strips offiber glass with a layer of copper coated thereon. An enlarged sideelevation view of the upper end of the spring 127 is shown in FIG. 9,showing the ber glass 260, and the copper conductor 261 deposited on thefiber glass 260. Also shown is the conductor 124 welded to the copperconductor 261. The layer of copper provides an electrical currentcarrying path between the ends of the spring. The fiber glass withstandscompression and tension forces when the hammer assembly is actuated intoand out of a printing position and, in addition, provides a springreturn which normally tends to retract the hammer assembly to theposition shown in FIG. 3. The ends of the coil 124 are shown connectedto the ends of the springs 127 and 128 by the dashed lines in FIG. 3.

The springs 127 and 128 are electrically connected to pins 133 and 134by means of electrical conductors shown in dashed lines. With referenceto FIGS. 1 and 2 it will be seen that the pins 133 and 134 mate withreceptacles 31 formed in connector blocks 30 and 32 which are po- 6sitioned on either side of the row of hammer assemblies 100.

The receptacles 31 provide an electrical connection to the connectorpins of each of the hammer assemblies from the electrical hammer drivingcircuits. The receptacles 31 in the connector blocks 30 and 32 areindividually and electrically connected to a twenty-pin connector 34 towhich the energizing current for the coils is applied. Although aseparate connection is indicated from each of receptacles 31 to theconnector 34, in one embodiment of the invention all receptacles areelectrically connected together and connected to one pin of theconnector 34.

Included in each of the hammer assemblies of rows and 200 and attachedto the shoulder of each hammer assembly is a hammer stop device.Referring to FIG. 3, the print hammer assembly 101 has a hammer stopdevice 250 which is attached to a shoulder 138 of the base structure 129by means of a bolt 251. The bolt 251 is threaded into the shoulder 138.The hammer stop device 250 has an adjustable member 252 against whichthe backend 123 of the elongated member 120 strikes as the elongatedmember is returned to rest from a printing operation. The position ofthe adjustable member 252 with respect to the drum 10 is adjusted bysetting the position of a bolt 254 which is threaded into the stopdevice 250.

Similar to the shoulder 138 the base structure 129 of the hammerassembly 101 has a shoulder 139. The shoulders 138 and 139 have keys 140and 142 which slide a short distance into the groove in between theadjacent support members and thereby provide a rigid supportingstructure for the hammer assembly. The keys 140 and 142 of the hammerassembly 101 are shown inserted in the gap 101a in FIG. 1 and areindicated by dashed lines.

The base structure 129 has a protrusion adjacent to which a locking hole132 is formed. An elongated locking hole 36 (see FIGS. 1 and 2) is alsoprovided along the length of the module base 24 and is aligned with thelocking hole in hammer assembly as well as a corresponding locking holein each of the other hammer assemblies. A locking pin 37 is insertedthrough the elongated locking hole 36 in the module base 24 and throughthe locking holes of each of the hammer assemblies in row 100. In thismanner each of the hammer assemblies is rigidly secured to the modulebase 24.

In the preferred embodiment of the present invention the elongatedmember and the coils of the hammer assemblies weigh about 1.2 g. Theweight of the elongated member and coil is important in causing thehammer to strike the drum with an acceptable energy level. Althoughhammer assembly 120 has been described by way of example, each of theother hammer assemblies in the lower row 100 as well as thoseV in theupper row 300 are identical to hammer assembly 120.

With the hammer assemblies in mind, consider specirically the novelmagnetic means for operation of the hammer assemblies. The magnets inthe preferred embodiment of the invention are of the type made by theIndiana Steel Company, a division of Indiana General Corporation, andidentified by the name INDOX V. INDOX V is a permanent ceramic magnetmade out of a highly orientated barilun ferrite matreial. The moreimportant characteristics of INDOX V, to the invention described herein,vare a high peak energy product of approximately 3.5 million, anextremely high coercive force, low weight and a low incrementalpermeability. The high coercive force of INDOX V makes possible the useof a much shorter magnetic path length than is possible' with previouslyused permanent magnets such as the type commonly referred to asv ALNICOV, and yet on an equivalent weight basis INDOX V Imagnets have an energyproduct comparable with ALNICO V magnets.

Demagnetizing fields are applied to the magnets by the coils of thehammer assemblies, during energization of the coils. The low incrementalpermeability characteristic of the INDOX V magnet causes it to provide avery constant magnetic field when subjected to external demagnetizingfields. `One of the most outstanding characteristics of INDOX V magnetsto the present invention is that the magnets are naturally mostefficient with a very short magnetic path length and a large activemagnetic gap area. This characteristic enables the magnets to bemagnetized through the thin dimension of the magnet from one gap to theother and thereby'allows one magnet, in conjunction with its twoIadjacent magnets,

to provide a magnetic field for two adjacent coils. This feature allowsthe magnets to be spaced very close together. Although INDOX V magnetsare described by way of example, it should be understood that othermagnets having characteristics similar to those -outlined hereinabovemay be used within the scope of the present invention.

FIG. is a side elevation view of the row of magnets 200 and the c-oilsof the hammer assemblies in row 100 which are shown with the elongate-dmember and supporting means removed. FIG. 6 is Ia cross-sectional viewof the magnets and coils shown in FIG. 5 taken along the lines 6 6 butshowing only the magnets 201 through 204 and the coils of the hammerassemblies 101, 102 and 103. FIG. 7 is a side elevation view of themagnet 201.

The magnets are magneti'zed over active areas and the fields of themagnets are parallel with the axes of the coils. This also makes thedirection of magnetization normal to the parallel surfaces, in the gaps,at either side of the magnets as shown by dashed lines in FIG. 6. Withreferenceto FIG. 6 it will be seen that a north pole magnetic iield isformed in one gap and a south pole magnetic eld is formed at theopposite side of a magnet' in the adjacent gap. -It should also be notedthat all of the magnets are magnetically poled in one direction,

namely, from south to north moving from right to left,

along one side of the row of magnets while the magnets are poled in theopposite direction, namely, north to south moving lfrom right to left,along the opposite side of the row of magnets. Thus, within each gap themagnetic field at one side of the row of magnets is poled in theopposite direction from the magnetic field in gap at the opposite sideof the row of magnets. The active magnetic areas at each side of themagnets are slightly larger than the width of one side of a coil and areillustrated by dashed lines in FIG. 6 and the dotted areas in FIG. 5.

The coils are positioned in relation to the magnets such that one sideof the coil is positioned in the active magnetic area of a gap towardsone side of the row of magnets and the other side of the coil ispositioned in the active magnetic area near the opposite side of the rowof magnets. In this manner all the current which flows in the onedirection (i.e. in an upward direction as shown in FIG. 5 is in amagnetically active area which is poled in one direction, whereas theother side of the coil in which current flows in the opposite direction(i.e. in a downward `direction as shown in FIG. 5)l is in the otheractive magnetic area of the cores in which the field is poled in theopposite direction. With this configuration, current applied in the coilof one of the Vhammer assemblies causes a iiow of electrons through theYcoil which interacts with the magnetic field in the corresponding gapcausing .a force on the coil which moves it. The coil is forced to movein between the two adjacent magnets either toward or away from thesurfaces of the drum, depending on the direction of the current in thecoil. Since the elongated member is connected to the coil, the hammertip is forced to strike -the surface of the drum whenever the current inthe coil is in such a direction that the magnet is forced to move in thedirection ofthe drum.

Table I shows the dimensions of the coils and mag-4 nets of a preferredembodiment of the present invention.

The dimensions shown in rFable I are identiiied in FIGS. 5, 6 and 7.

An important feature of the present invention is that the magnets andcorresponding coils are all aligned in astraight row parallel with thesurface of the drum. This is in contrast to the prior art wherein themagnets and coils `are staggered in depth. In order to make the spacingbetween hammer assemblies short enough so that staggering can beeliminated with the standard center to center hammer spacing of .1 inch,it has been found that the ratio of the length of the air gap in betweenadjacent magnets, i.e. dimension 509 in FIG. 6, to the total magneticpath length, (including the magnetic path length of the magnet plus theair gap length,) i.e. dimension 50S in FIG. 6, should be 1/5 or greaterwith a flux density over the active .area of the magnets of 1,000 gaussor greater. This is in marked contrast to the prior art wherein theratio of air gap length to tota-l magnetic path length is in the orderof 1/14, with higher flux density but a correspondingly greater hammermass due to increased length of the hammer.

FIG. 8 shows a sketch of a prior art hammer actuating mechanism showingthree coils and the corresponding magnets. The view of the prior artdevice as shown in FIG. 8 is a cross sectioned view taken similar to theview Of the present invention as shown in FIG. 6. The prior art magnetsare referenced by the symbols 50 through 55 and are U shaped magnets.The magnets 50 through 55 are shown with coils 56, 57 and 58 of thehammer assemblies (the rest of which are not shown) in between the endsof the legsof the magnets. In one embodiment ofthe improved prior artprinter the total magnetic path (including the magnetic path length ofthe magnet plus the air gapV length), which is indicated by dashed line53 in FIG-8, is approximately 14/16 inches long, whereas the dimensionsof the gap is between the end of the legs of two adjacent magnets isapproximately 1/16 inches. Thus,

'that as the elongated member increases in length, the

time for the shock wave to travel from the backend of the elongatedmember to the hammer, and back again, increases. To this end it has beenfound that greatly increased speed can be achieved by limiting thelength of the elongated member, as shown in the drawings, so

that it is at least as `long as the width of the coil connected theretobut shorter in length than twice the width of the coil.

The upper row of hammer assemblies 300 and upper u row of magnets 400are constructed and assembled essentially the same as the lower rows and200. The individual hammer assemblies in row 300 are identical to thehammer assemblies in row 100 and moving from `right to left in FIG. 2are referenced by the symbols 301 through 310.

401 through 411. (Only the first two magnets 401 and 402 and the lastmagnet 411 in the row have their reference -numbers shown in FIG. 2.)The magnets 401 through 411 are identical to the magnets 201 through 211and, moving from right to left in FIG. 2, -are arranged to provideslot-shaped gaps 301e: through 31% for the hammer assemblies 301 through310. (Only gaps 301e, 302e, and 310e: have their reference numbers shownin FIG. 2.) Similar to the lower row of magnets 200, the upper row ofmagnets 400` are rigidly cemented in between upstanding support arms.The upstanding supp-ort arms, moving from right to left in FIG. 2, arereferenced by the symbols 401er through 411a. (Only the support arms401m 402er and 41161 have their reference numbers shown in FIG. 2.) Thesupport arms 401e through 411e are formed as an integral part of amodule base 26 which is connected to the base structure 2S by means of abolt 26h similar to module base 24.

The upper roW of hammer assemblies 300, the upper row of magnets 400:,and the module base 26 are identical to the lower rows 100 and 200 andthe module base 24 but are upside' down and displaced .slightly withrespect to the lower rows 100 and 200 and the lower module base 24 sothat the elongated members of the hammer assemblies in the upper now300` fall in between the elongated members of the hammer assemblies inthe lower row 100. Thus, a gap between a pair of adjacent magnets in theupper row of magnets 400 -coincides with the middle of `a magnet in thelower row of magnets 200.

The module base 26 is rigidly secured to the frame 25 by means of a bolt26b which is threaded into a riser 26C of the module base 26. Similar tothe connector blocks and connector 34 connector blocks 40 and 41 and aconnector 42 are provided for the same purpose for the upper row ofhammer assemblies 200.

As a general rule, printers have l2() character positions in a line ofprint, with a center t-o center spacing of the hammers of .l inch. Thecenter to center spacing in the lower row is .2 inch. Therefore, theupper row of hammer assemblies 300 is added to provide the desiredcenter to center spacing of .l inch. It will be understood thatadditional modules may be added to the module of hammer assemblies andmagnets shown in FIGS. l and 2 until the total complement of 120 hammerassemblies are obtained for a complete line of print 120` characterpositions. It should also be noted that the individual hammer assembliesare identical and are easily plugged and removed from the connectorblocks. This feature greatly simplifies maintenance by allowing hammerassemblies to be replaced easily and rapidly as desired. Also,`theentire module base 24, magnets 200 Iand hammer assemblies 100y can beremoved from the printer frame 25 simply by removing fthe bolt 24b. Thisfeature also facilitates easy maintenance and repair of the printer.

Consider the operatio-n of the printer. Whenever it is 1desired to forceone of the hammers into a printing position with the drum 10, current isapplied through one of the connectors 34 and 42 to a pair of wiresrunning to the corresponding hammer assembly. The current passes throughto the receptacle of one of the connector blocks 30 and 32 up throughthe spring of the hammer assembly, `through the coil, and back outthrough the coil to the other spring. The current passes through theother spring through the other connector block, back to the connector.The current in the coil is such that it causes an interaction with themagnets on either side of the coil causing the coil and the elongatedmember to -be forced towards the rotating drum 10. The hammer tip of theelongated member strikes the paper causing the character in front of thehammer tip to be used to make an imprint on the paper.

The hammer assembly is returned to its normal deactivated position byapplying acurrent through the coil in the opposite direction. Thiscauses the coil and con- 10 nected elongated member to be forced back inthe opposite direction until it is stopped by the corresponding hammerstop.

It will be understood that there is a separate hammer driver circuit(not shown) for each hammer assembly in the printer so that one or morehammer assemblies may be actuated simultaneously.

What is claimed is:

1. A printing `device comprising: a rotatable type drum; a plurality ofparallelepiped shaped ceramic magnets positioned in a substantiallystraight row parallel with the axis of said type drum, each of saidmagnets cooperating with the adjacent magnet, at both sides, to defineslot-shaped gaps therebetween; and a hammer assembly for each gapcomprising an elongated member having a hammer tip at one end, asubstantially flat coil mechanically connected intermediate the ends ofsaid member with the axis of the coil perpendicular' to the elongationof said member and means including a pair of atsprings connected to thehammer assembly and adapted `for supporting each hammer assembly suchthat the coil is free to move in the corresponding gap to- Ward and awayfrom the surface of said drum, the springs comprising an electricallyconductive material and connected to the ends of said coil for providingan electrical current path thereto, the magnets being magnetizedparallel to the axes Iof the coils so that current applied through thesprings to a particular coil causes a force between the coil andadjacent magnets forcing the hammer tip of the connected member into aprinting position with the drum.

2. A printing device comprising: movable type bearing means; a pluralityof permanent magnets positioned in a substantiallly straight row, eachof said magnets having a pair of parallel and substantially flatsurfaces arranged with respect to the adjacent magnet, at both sides, todefine slot-shaped gaps therebetween; and a hammer assembly for each gapcomprising `an elongated member having a hammer tip at one end, asubstantially flat coil mechanically connected intermediate the ends ofsaid member with the axis `of the coil perpendicular to the elongationof said member and means adapted for supporting each hammer assemblysuch that the coil is free to move in the corresponding gap toward andaway from the type bearing means, the magnets being magnetized parallel`to the axes of the coils so that current applied in a coil causes aforce between the coil and adjacent magnets forcing the hammer tip ofthe connected member into a printing position with the type bearingmeans.

3. A printing device comprising: a rotatable type drum; a plurality ofhammer assemblies each comprising an elongated member having a hammertip at one end thereof and a substantially flat coil mechanicallyconnected intermediate the ends of said elongated member with the axisof the coil perpendicular to the member; means for supporting theelongated members and the connected coils with the coils spaced a shortprefixed distance apart and in a substantially straight row parallelwith `the axis of said drum, said mounting means being adapted to allowthe hammer assemblies to move the hammers thereof into a printingposition with respect to the drum; and a parallelepiped shaped ceramicmagnet having a thin dimension positioned in between each adjacent pair`of coils, said magnets being magnetized through the thin dimension in adirection parallel with the axes of said Lcoils such that a magneticinteraction is caused which forces a coil to move, in the correspondinggap, so that the connected hammer tip is forced into a printing positionwith respect to said drum, Ain response to current applied in theparticular coil.

4. A printing device as dened in `claim 3 wherein each hammer assemblyis characterized whereby the coil thereof has an overall widthdimension, parallel with the elongated extension of said member, thedimension of said elongated member parallel with the elongated extensionthereof being greater than said outside width dimension but less thantwice as long as said outside width dimension. 5. A printing device asdefined in claim t wherein said supporting means comprises a supportstructure and a pair of substantially parallel flat springs connectedbetween the base structure and the elongated member.

6. A printing device comprising: movable type bearing means; a pluralityof hammer assemblies comprising a hammer tool and a substantially fiatcoil mechanically connected to said hammer tool; means for supportingthe hammer tools and connected coils of said hammer assemblies with thecoils spaced a short prefixed distance apart with the axis of each coilpositioned in a substantially straight line, said mounting means beingadapted to allow the hammer assemblies to move the hammer tool thereofinto a printing position with respect to the type bearing means; and athin ceramic magnet positioned in between each adjacent pair of coils,said magnets having a pair of substantially fiat surfaces facing theadjacent magnets which are separated by the thin dimension thereof andbeing magnetized -through the thin dimension in a direction parallel tothe axis of said coils such that a magnetic interaction is caused whichforces the coil to ymove in the corresponding gap so that thecorresponding hammer tool is forced into a printing position withrespect to said type bearing means, in response to current applied tothe particular coil.

7. A printing device comprising: a rotatable type drum;

a plurality of parallelepiped shaped ceramic magnets posi` tioned in asubstantially straight row parallel with the axis of said type drum,each of said magnets cooperating with the adjacent magnet, at bothsides, to define slotshaped gaps therebetween; and a hammer -assemblyfor each gap comprising an elongated member having a hammer Itip at oneend, a substantially fiat coil mechanically connected intermediate theends of said member with the axis of the coil perpendicular to theelongation of said member and means adapted for supporting each hammerassembly such that the coil is free to to move in the corresponding gaptoward and away from the surface of said drum, the magnets beingmagnetized parallel with the axes of the coils such that a north polemagnetic field is formed in one gap and a south pole magnetic field isformed in the adjacent gap, all the magnets being magnetically poled inone direction along one side of the row of magnets and in theoppositedirection along the opposite side of the row of magnets, the coils beingpositioned in relation to the poles of the magnets such that a force iscaused between a coil and the corresponding magnets, responsive tocurrent applied in the coil, for forcing the hammer tip of the connectedmember into a printing position with the drum.

8. A printing device as defined in claim 7 including a support structureand wherein saidsupporting means comprises a pair of fiat suspensionsprings mechanically connected in parallel between the support structureand the elongated member at either side of the connected coil.

9. A printing device as defined in claim 8 wherein said suspensionspringscomprise an electrically conductive malteri-al and are connectedto opposite ends of said coil for providing electrical current thereto.

10. A printing device comprising: type bearing means;l

a plurality of ceramic magnets positioned in a substantially straightrow, each of said magnets having two substantially fiat parallelsurfaces separated by a thin dimension and facing the adjacent magnet,at both sides, to define slot-shaped gaps therebetween; a hammerassembly for each gap comprising an elongated member having a hammer tipat one end and a substantially fiat coil mechanically connectedintermediate the ends of said member with the axis of the coilperpendicular to the elongation of said member; and means adapted forsupporting each hammer assembly such that the coil is free to move inthe corresponding gap toward and away from said type bearing means, themagnets being magnetized through the thin dimensions parallel with theaxes of the coils such that a north pole magnetic field is formed in onegap and a south pole magnetic field is formed in the adjacent gap, allthe magnets being magnetically poled in one direction along one side ofthe row of magnets and in the opposite direction along the oppositeVside of the row of magnets, the coils being positioned invrelation tothe poles of the magnets such that a force is caused between a coil andthe corresponding magnets, responsive to current applied in the coil,for forcing the hammer tip of the connected member into a printingposition with the type bearing means.

il. Assembly for a printing apparatus comprising: a plurality ofpermanent magnets positioned in a substantially straight row, each ofsaid magnets having a pair of parallel surfaces separated by a thindimension and facing the adjacent magnet, at both sides, to defineslot-shaped gaps therebetween; a hammer assembly for each gap comprisinga hammer tool and a substantially fiat coil mechanically connected tosaid hammer tool; and means adapted for supporting the hammer-assemblies with the axes of the coils thereof in a substantiallystraight line perpendicular to said surfaces of the magnets such thatthe coil is free to move in the corresponding gaps toward and away froma predetermined point of impact, the magnets being magnetized throughthe thin dimension thereof parallel with the axes ofthe coils such thata north pole magnetic field is formed in one gap and a south polemagnetic field is form'ed in the adjacent gap, all of the magnets beingmagnetically poled in one direction along one side of the row of magnetsand in the opposite direction along the opposite side of the row ofmagnets, the coils being positioned in relation to the poles of themagnets such that a Vforce is caused between a coil and thecorrespondingmagnets, responsive to current applied in the coil, forforcing the connected hammer tool into such point of impact. 1'

12. A printing device comprising: type bearing means; a plurality ofpermanent magnets positioned in a substantially straight row, each ofsaid magnets having first and second substantially fiat and parallelsurfaces separated by a thin dimension and facing the adjacent magnet,at both sides, to define slot-shaped gaps therebetween, said row ofmagnets having first and second sides, the dimension therebetween beingsubstantially larger than said thin dimension, the magnets beingmagnetized over an active area adjacent said first side normal to saidfirst and second surfaces with a north pole at said first surface and asouth pole at said second surface, the magnets being magnetized over anactive area adjacent said second side normal to said first and secondsurfaces with a south pole at said first surface and a north pole atsaid second surface; a hammer assembly for each gap comprising a harnmertool and a substantially fiat coil mechanically connected to said hammertool; and means adapted for supporting each hammer assembly with thecoil in the corresponding gap and the axis of the coil normal to saidparallel surfaces such that the coil is free to move in thecorresponding gap toward and away from said type bearing means, eachcoil being positioned in relation to active areas of the magnets suchthat a force is caused between the coil and the corresponding magnets,responsive to current applied in the coil, for forcing the connectedhammer tool into a printing position with the type bearing means.

13. A printing device comprising: type bearing means; a plurality ofpermanent magnets positioned in a substantially straight row, each ofsaid magnets having a pair of substantially fiat surfaces facing theadjacent magnet, on both sides, which are parallel with the'corresponding surfaces of the adjacent magnets to define slot-shapedgaps therebetween, each magnet being magnetized in a straight linenormally to the surfaces thereof and characterized and positioned inrelation to the adjacent magnet with a f ratio of air gap length to airgap length plus magnetic path i3 length of the magnet of at least 1%;and for providing a ilux density'over an active area of the magnetsurfaces of at least 1000 gauss; a hammer assemblyfor each gapcomprising a hammer tool, a substantially at coil mechanically connectedto said hammer tool; and means adapted for supporting the hammerassembly such that the coil is in the corresponding gap with the axis ofthe coil perpendicular to the magnet surfaces on either side, the sup'port means being adapted to allow the coil to move in the correspondinggap toward and away from the type bearing means, the coils beingpositioned in relation to the active areas of the magnets such that aforce is caused between the coil and the corresponding magnets,responsive to current applied in the coil, for forcing the connectedhammer tool into a printing position with the type bearing means.

14. A printing device comprising: a rotatable type drum a plurality ofparallelepiped shaped ceramic magnets having sides and positioned in `asubstantially straight row parallel with the axis of said type drum,each of said magnets cooperating with the adjacent magnet, at bothsides, to dene slot-shaped gaps therebetween; connector means includingan electrical connector at each side of each of said gaps; and apluggable hammer assembly for each gap comprising an elongated memberhaving a hammer tip at one end, a substantially flat coil mechanicallyconnected intermediate the ends of said member with the axis of the coilperpendicular to the elongation of said member, a hammer assembly basestructure, a pair of flat springs connected between the hammer basestructure and the elongated member and adapted for supporting each tormeans being electrically connected to the conductive material of one ofsaid springs, the magnets being magnetized parallel to the axes of thecoils so that current applied through the springs to a particular coilcauses a force between the coil and the adjacent magnets forcing thehammer tip of the connected member into a printing position with thedrum.

15. A -printing device as defined in claim 14 having means comprising apair of support arms rigidly attached at the sides of each magnet forthereby securely holding each magnet in place with respect to the othermagnets.

References Cited by the Examiner UNITED STATES PATENTS 3,145,650 8/1964Wright l0l-93 3,164,084 l/l965 Paige lOl-93 3,172,352 3/1965 HelmslOl-93 WILLIAM B. PENN, Primary Examinez'.

1. A PRINTING DEVICE COMPRISING: A ROTATABLE TYPE DRUM; A PLURALITY OFPARALLELEPIPED SHAPED CERAMIC MAGNETS POSITIONED IN A SUBSTANTIALLYSTRAIGHT ROW PARALLEL WITH THE AXIS OF SAID TYPE DRUM, EACH OF SAIDMAGNETS COOPERATING WITH THE ADJACENT MAGNET, AT BOTH SIDES, TO DEFINESLOT-SHAPED GAPS THEREBETWEEN; AND A HAMMER ASSEMBLY FOR EACH GAPCOMPRISING AN ELONGATED MEMBER HAVING A HAMMER TIP AT ONE END, ASUBSTANTIALLY FLAT COIL MECHANICALLY CONNECTED INTERMEDIATE THE ENDS OFTHE MEMBER WITH THE AXIS OF THE COIL PERPENDICULAR TO THE ELONGATION OFSAID MEMBER AND MEANS INCLUDING A PAIR OF FLATSPRINGS CONNECTED TO THEHAMMER ASSEMBLY AND ADAPTED FOR SUPPORTING EACH HAMMER ASSEMBLY SUCHTHAT THE COIL IS FREE TO MOVE IN THE CORRESPONDING GAP TOWARD AND AWAYFROM THE SURFACE OF SAID DRUM, THE SPRINGS COMPRISING AN ELECTRICALLYCONDUCTIVE MATERIAL AND CONNECTED TO THE ENDS OF SAID COIL FOR PROVIDINGAN ELECTRICAL CURRENT PATH THERETO, THE MAGNETS BEING MAGNETIZEDPARALLEL TO THE AXES OF THE COILS SO THAT CURRENT APPLIED